TW201307451A - Cellulose triacetate films with low birefringence - Google Patents

Abstract

The present invention relates to films made from cellulose tricacetate having low hydroxyl content and certain plasticizers. These films can exhibit low or zero optical retardation values, making them particularly suitable for use in optical applications, such as in liquid crystal displays (LCD) as protective and compensator films.

Description

Cellulose triacetate film with low birefringence

In general, the present invention relates to films made from cellulose triacetate having a low hydroxyl content and certain plasticizers, and methods of making the films. These films can exhibit low birefringence, which makes them particularly suitable for use in optical applications, such as in liquid crystal displays (LCDs) as protective and compensation films.

Cellulose esters such as cellulose triacetate (CTA or TAC), cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) are used in various films by the liquid crystal display (LCD) industry. Most notably, it is used as a protective or compensation film together with a polarizing plate, as described, for example, in US 2009/0068381 A1, the entire disclosure of which is incorporated herein by reference. The films are typically prepared by solvent casting and then laminated to either side of a oriented iodinated polyvinyl alcohol (PVOH or PVA) polarizing film to protect the PVOH layer from scratches and moisture ingress. At the same time, it also increases structural rigidity. Alternatively, as in the case of a compensation film, it may be laminated with the polarizer stack or otherwise included between the polarizer and the liquid crystal layer. Cellulose esters can have many of the performance advantages over other materials used in display films (e.g., cyclic olefins, polycarbonates, polyimines, etc.).

In addition to protection, these films can also play a role in improving the contrast ratio, wide viewing angle, and color shift performance of LCDs. For a typical set of crossed polarizers used in LCDs, especially when the viewing angle is increased, there is significant light leakage along the diagonal (which results in a poor contrast ratio). It is known that various combinations of optical films can be used to correct or "compensate" for this light leakage. These membranes must have a certain The defined birefringence (or retardation) varies depending on the type of liquid crystal cell used, since the liquid crystal cell itself will also impart a degree of undesirable optical retardation that must be corrected. Some of these compensating membranes are easier to prepare than others, often resulting in a compromise between performance and cost. Moreover, while most compensation and protective films are prepared by solvent casting, the industry is striving to produce more films by melt extrusion.

The compensation and optical film are typically quantified in the form of birefringence associated with refractive index n. In general, the refractive index of the polymer is typically in the range of from 1.4 to 1.8, and the refractive index of the cellulose ester is from about 1.46 to 1.50. For a given material, the higher the refractive index, the slower the light travels through it.

For an unoriented isotropic material, the refractive index will be the same regardless of the polarization state of the incoming light wave. As the material becomes oriented or otherwise becomes anisotropic, the refractive index becomes dependent on the material direction. For the purposes of the present invention, there are three refractive indices of interest expressed as n _x , n _{y ,} and n _z , which correspond to machine direction (MD), lateral direction (TD), and thickness direction, respectively. As the material becomes more anisotropic (eg, by stretching it), the difference between any two refractive indices will increase. This difference is called "birefringence".

Since there are many combinations of selectable material directions, different birefringence values exist accordingly. The two most common birefringence plane birefringences Δn _e and thickness birefringence Δn _th are defined as follows: (1a) Δn _e = n _{x -} n _y ; and (1b) Δn _th = [n _z - ( n _x +n _y )]/2.

The birefringence Δn _e is a measure of the relative in-plane orientation between MD and TD and is dimensionless. In contrast, Δn _th gives a measure of the orientation of the thickness direction relative to the average plane orientation.

Another term often used to characterize optical films is optical retardation (R). R is simply the birefringence multiplied by the thickness (d) of the film in question. Therefore, (2a)R _e =Δn _e d=(n _x -n _y )*d; and (2b)R _th =Δn _th d=[n _z -(n _x +n _y )/2]* d.

Latency is a direct measure of the relative phase shift between two orthogonal optical waves and is typically reported in units of nanometers (nm). It should be noted that the definition of _Rth , especially with respect to the +/- symbol, will vary with some authors.

It is also known that the birefringence/delay behavior of a material changes. For example, most materials will exhibit a higher index of refraction in the direction of stretching when stretched and a lower index of refraction in the direction perpendicular to the direction of stretching. This is because, at the molecular level, the refractive index is generally higher along the axis of the polymer chain and lower perpendicular to the chain. These materials are commonly referred to as "positive birefringence" and represent most standard polymers, including all commercially available cellulose esters.

Another useful parameter is "inherent birefringence," which is a measure of the nature of the material and is a measure of birefringence that would occur if the material was sufficiently stretched and all chains were perfectly aligned in one direction.

There are two other less rare types of materials, namely "negative birefringence" and "zero birefringence". The negative birefringent polymer exhibits a higher refractive index in a direction perpendicular to the stretching direction (relative to the parallel direction), and thus also has a negative intrinsic birefringence. Certain styrenics and acrylics are known to have negative birefringence behavior due to their relatively bulky pendant groups. In contrast, zero birefringence is a special case and represents a material that does not exhibit birefringence when stretched and therefore has zero intrinsic birefringence. These materials are ideal for optical applications because they can be used everywhere Molding, stretching, or otherwise applying stress during the process without exhibiting any optical retardation or distortion. These materials are also extremely rare.

For the compensation film, in order to properly eliminate light leakage, it must be combined in some manner depending on the type of liquid crystal cell used. For example, Fundamentals of Liquid Crystal Displays (DKYang and STWu, Wiley, New Jersey, 2006, pp. 208-237) illustrates a variety of ways to use a combination of single-axis plates (two-axis plates are also effective but mathematically complex). To compensate for IPS (in-plane switching), twisted nematic (TN) and VA (vertical alignment) type units. In the case of an IPS unit, a low retardation film is more effective for minimizing light leakage than conventional cellulose acetate membranes.

For example, when the backlight passes through the two conventional triacetyl cellulose (TAC) film (having both R _e = 0 nm and R _th = -40 nm) of the orthogonal polarizers, one pair of light transmission calculated The contour plot shows approximately 2.2% light leakage at 45° along the transmission axis of the polarizer.

On the other hand, when the backlight passes through a pair of crossed polarizers with two zero-delay TAC films (both with R _e =0 nm and R _th =0 nm), the contour map of the calculated light transmission is shown along the There is a light leakage of a maximum of about 1.3% at 45° of the transmission axis of the polarizer.

Thus, by replacing the two conventional TAC films with two zero-delay TAC films, light leakage can be reduced by almost half.

Furthermore, one advantage of using a cellulose ester based zero retardation film over a non-cellulose ester based zero retardation film is that the cellulose ester based film adheres well to the PVA. Therefore, the current polarizer processing program will not be affected.

Unfortunately, typical solvent cast triacetate membranes typically have _Rth values ranging from about -20 nm to -70 nm. Accordingly, there is a need in the art to provide a cellulose triacetate film having a lower retardation, preferably zero or near zero retardation, to improve the compensation film performance of an LCD operating in IPS mode.

The present invention meets this need and other needs, and the scope of the following description and the accompanying claims will become apparent.

It has been surprisingly found that a cellulose triacetate film having a low or zero optical retardation in the thickness direction can be prepared. These films are especially useful as LCD compensation films.

In one aspect, the invention provides a film comprising: (a) cellulose triacetate having an acetylation degree of substitution (DS _{ethyl ketone group} ) of from 2.8 to 2.95; and (b) based on the total weight of the film, 5 to 15% by weight of a plasticizer selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester amber Acid ester, butyl benzene sulfonamide, camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, octyl epoxidized octyl ester, Polyethylene glycol, tris(ethylene glycol) bis(2-ethylhexanoate), and mixtures thereof. The film has been annealed at a temperature of from 100 ° C to 140 ° C for at least 60 minutes. Further, when measured at a wavelength of 589 nm and normalized to a film thickness of 60 μm or less, the film has an optical retardation value (R _th ) in the thickness direction of -15 nm to +15 nm.

In a second aspect, the invention provides a method of making a film. The method comprises the steps of: (a) forming a dopant comprising: (i) cellulose triacetate having an acetylation degree of substitution (DS _{ethyl thiol} ) of from 2.8 to 2.95; (ii) plasticizing a agent selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate, butyl sulfonamide, Camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, octyl epoxide, polyethylene glycol, tris(ethylene glycol) a bis(2-ethylhexanoate) and mixtures thereof; and (iii) a solvent; (b) casting the dopant onto the surface to form a wet film; (c) evaporating at least a portion of the solvent from the wet film To form a dry film; and (d) annealing the dry film at a temperature of 100 ° C to 140 ° C for at least 60 minutes to form a final film. The final film comprises from 5% by weight to 15% by weight, based on the total weight of the film, of a plasticizer. When measured at a wavelength of 589 nm and normalized to a film thickness of 60 μm or less, the optical retardation value (R _th ) of the final film in the thickness direction is also -15 nm to +15 nm.

According to the present invention, there is provided a film comprising: (a) cellulose triacetate having a degree of substitution of ethylene (DS _{ethyl ketone} ) of from 2.8 to 2.95; and (b) 5% by weight based on the total weight of the film 15% by weight of a plasticizer selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate, butyl Benzosulfonamide, camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, octyl epoxidized octyl ester, polyethylene glycol , tris(ethylene glycol) bis(2-ethylhexanoate) and mixtures thereof.

The film has been annealed at a temperature of from 100 ° C to 140 ° C for at least 60 minutes.

Further, when measured at a wavelength of 589 nm and normalized to a film thickness of 60 μm or less, the film has an optical retardation value (R _th ) in the thickness direction of -15 nm to +15 nm.

In one embodiment, the film has an _Rth value in the range of -10 nm to +10 nm. In another embodiment, the film has an _Rth value in the range of -5 nm to +5 nm. Other _Rth values within such general ranges are also encompassed within the scope of the invention, such as -3 nm to +3 nm.

The thickness of the film of the invention can vary depending on the application. For example, typically for LCD applications, the film thickness can range from 40 μιη to 100 μιη. Other film thicknesses range from 40 μm to 80 μm and 40 μm to 60 μm.

The cellulose triacetate (CTA) used in the film of the present invention has an ethyl sulfhydryl substitution degree (DS _{acetyl group} ) of 2.8 to 2.95. This corresponds to a DS _{OH of} 0.05 to 0.2. The cellulose triacetate having this DS _{ethyl oxime} is commercially available from suppliers such as Eastman Chemical.

The film typically contains from 85 wt% to 95 wt% CTA, based on the total weight of the film. In some embodiments, the film may contain from 85 wt% to 90 wt% or from 90 wt% to 95 wt% CTA.

The plasticizer of the present invention is selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate (example) Such as Resoflex® 804), butyl sulfonamide, camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate (eg Resoflex® 296 or Paraplex® G-50), epoxidized octyl talate (eg Drapex® 4.4), polyethylene glycol (eg PEG 400 or 600) and tris(ethylene glycol) bis(2-ethylhexanoate). These plasticizers are commercially available.

The amount of plasticizer in the composition can vary depending on the particular plasticizer used, the annealing conditions employed, and the desired _Rth value. Generally, the plasticizer may be present in an amount ranging from 5 wt% to 15 wt%, based on the total weight of the film. The plasticizer may also be present in an amount from 5% by weight to 10% by weight or from 10% by weight to 15% by weight.

In addition to the plasticizer, the film of the present invention may also contain additives such as stabilizers, UV absorbers, anti-caking agents, slip additives, lubricants, pinning agents, dyes, pigments, delayed modification. Agent, matting agent, mold release agent, etc.

The invention also provides a method of making a film. The method comprises the steps of: (a) forming a dopant comprising: (i) cellulose triacetate having a degree of substitution of ethylene (DS _{ethyl thiol} ) of from 2.8 to 2.95; (ii) a plasticizer. Selected from the following groups: sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate, butyl sulfonamide, camphor, 2 , 2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, octyl epoxidized octyl ester, polyethylene glycol, tris(ethylene glycol) bis ( 2-ethylhexanoate) and mixtures thereof; and (iii) a solvent; (b) casting the dopant onto a surface to form a wet film; (c) evaporating at least a portion of the solvent from the wet film to form a dry And (d) annealing the dry film at a temperature of from 100 ° C to 140 ° C for at least 60 minutes to form a final film.

The final film comprises from 5% by weight to 15% by weight, based on the total weight of the film, of a plasticizer.

When measured at a wavelength of 589 nm and normalized to a film thickness of 60 μm or less, the optical retardation value (R _th ) of the final film in the thickness direction is also -15 nm to +15 nm.

The CTA, plasticizer and solvent can be combined in any manner to form a dopant. For example, CTA and plasticizer can be combined together and then added to the solvent. Alternatively, CTA and a plasticizer may be added to the solvent individually. After combining the components, the mixture should be thoroughly mixed to ensure substantially uniform casting of the dopant.

The solvent in which the CTA and the plasticizer are mixed is not particularly limited. It may be suitable for preparing a dopant to form any liquid of the CTA film by casting. Typical solvents include dichloromethane and alcohol. One such solvent is a 85/15 vol% mixture of dichloromethane and methanol or ethanol.

The resulting dopant can be cast onto a typical solvent casting apparatus such as a casting belt, a casting drum or a moving plastic film to form a wet film. The surfaces of the casting belt and the drum are usually made of stainless steel or chrome-plated steel. The surface of the moving plastic film can be made of PTFE or deuterated PET.

After casting, the wet film is subjected to an evaporation step to remove at least a portion of the solvent To the dry film. The dry film may have a residual solvent content of from 1% by weight to 50% by weight. In some embodiments, the residual solvent content can range from 3% to 40% by weight. In other embodiments, the residual solvent content of the dry film can range from 3% to 6% by weight.

The evaporation step can be carried out under ambient conditions. Alternatively, the evaporation step can be carried out at elevated temperatures (eg, from 25 ° C up to 100 ° C, from 30 ° C to 95 ° C or from 40 ° C to 80 ° C). A variety of methods can be used to facilitate evaporation, such as indirect heating, by radiant heating, and/or by controlled heating or solvent loaded controlled air flow.

After the evaporation step, the dry film can be removed from the cast surface and then annealed. Alternatively, the film can be annealed while casting on the surface. The annealing step can be carried out in one or more stages in any suitable equipment, such as in a forced air oven, for example at 100 ° C for up to 10 minutes and then at higher temperatures (eg 120 ° C, 130 ° C or 140 ° C) It lasts for 20 minutes. During annealing, the film can be restrained by any suitable means to prevent shrinkage.

After annealing, the residual solvent content of the film is typically less than 3% by weight. In some embodiments, the residual solvent content of the annealed film can be less than 1.5% by weight. In other embodiments, the residual solvent content of the annealed film can be less than 0.5% by weight.

Without wishing to be bound by theory, the primary purpose of the annealing step is to increase the diffusion of residual solvent that may remain in the film from the casting process. However, the additional benefit of annealing is to relax the residual stress generated during the casting process. When the film adheres to the cast substrate, the solvent evaporates to the open surface, creating internal stresses in the film. These stresses depend on material properties, solvent mixture, and Adhesion of the substrate and evaporation rate of the solvent. Casting methods and rates can result in higher stresses, higher birefringence, and higher retardation. For the manufacture of films having dimensional stability and low retardation, it is desirable to relax the stresses induced by such processes.

These annealing times and temperatures can vary depending on the casting technique used. For example, if a continuous solvent casting line is used instead of batch processing in a laboratory, a lower annealing temperature and a shorter time can be used.

The final film can be post-treated using methods well known in the art (e.g., corona treatment, plasma treatment, flame treatment, etc.). The film can also be saponified to ensure good adhesion to the subsequent PVOH polarizing layer.

The invention also provides a polarizing plate comprising a film as described herein. The present invention further provides a liquid crystal display including the polarizing plate. For liquid crystal display applications, the films of the present invention will eventually be combined with other films and structures to form a unitary liquid crystal device. Examples of methods used include lamination and/or coating. Such structures are well known to those skilled in the art, and it should be understood that the films of the present invention can be used in a variety of forms depending on the specifications of the particular manufacturer and the type of liquid crystal cell.

The invention is further illustrated by the following working examples, which are to be construed as being limited to the scope of the invention.

Instance Measuring procedure

Membrane optical retardation R _e and R _th were measured using a Woollam ellipsometer M-2000V with a wavelength range of 370 nm to 1000 nm. For comparison purposes, measurements were taken at 589 nm and the data was normalized to film thicknesses of 60 μm and 40 μm. This normalized delay is calculated as follows: R _th = target thickness * mR _th /d; and R _e = target thickness * mR _e / d where the mR _th film sample is measured R _th , mR _e film test The sample is measured by R _e and d is the actual film thickness (expressed in microns). The target film thickness is 60 μm or 40 μm. Two normalized data sets are included in the following examples.

material

All of these examples used the same commercially available cellulose triacetate (CTA) resin with a DS _{ethyl oxime} of about 2.86.

The following table identifies abbreviations for some of the plasticizers used in these examples.

Comparison example 1-16

The cellulose triacetate film was prepared by solvent casting using the following procedure: First, 24 g of solid (CTA resin + plasticizer identified in Table 1 below) was added. Add to 176 grams of a 85/15 vol% solvent mixture of dichloromethane/ethanol. The plasticizer was added at a load of 10 wt% based on the total weight of the solid. The mixture was then sealed, placed on a roll and mixed for 24 hours to produce a uniform dopant.

After mixing, the dopant was cast onto the glass plate using a doctor blade adjusted to a target thickness of 40 μm. Casting was carried out in a fume hood with a relative humidity control set at 50%.

After casting, the film and glass were dried under a covered pan for 1 hour. After this initial drying, the film was peeled from the glass and annealed at room temperature for 1 hour to several hours.

The optical retardation of the film is measured as a function of annealing time. The results are shown in Table 1.

Example 1-5

The cellulose triacetate film was prepared by solvent casting according to the procedure set forth in Comparative Examples 1-16 except that the casting solvent contained methanol instead of ethanol, the film target thickness was 60 μm, and the annealing step was carried out in a forced air oven. It was carried out at 100 ° C for 10 minutes and then at 120 ° C or 130 ° C for 20 minutes. Furthermore, annealing is performed with the film constrained to a pair of metal frames to prevent any further shrinkage.

The optical retardation of the film is measured as a function of annealing time. The results are also shown in Table 1.

Comparative Examples 17-24 and Examples 6-10

The cellulose triacetate film was prepared by solvent casting according to the procedure set forth in Comparative Examples 1-16 except that the casting solvent contained methanol instead of ethanol; the plasticizer loadings were 5 wt%, 7.5 wt%, and 10 wt%. The film thickness was 60 μm; and the annealing step was carried out in a forced air oven at 100 ° C for 10 minutes and then at 120 ° C for 20 minutes. In addition, in Annealing is performed with the film constrained to a pair of metal frames to prevent any further shrinkage.

After annealing, the optical retardation of the film was measured. The results are shown in Table 2.

Example 11-14

The cellulose triacetate film was prepared by solvent casting according to the procedure set forth in Comparative Examples 1-16 except that the annealing step was continued in a forced air oven at 100 ° C for 10 minutes and then at 120 ° C or 130 ° C. Implemented in 10 minutes. In addition, annealing is performed to confine the film to a pair of metal frames to prevent any further shrinkage.

After annealing, the optical retardation of the film was measured. The results are shown in Table 3. For the sake of convenience, the results from Examples 4 and 5 are also reproduced in Table 3.

Examples 15-24 and Comparative Examples 25-28

The cellulose triacetate film was prepared by solvent casting according to the procedure set forth in Comparative Examples 1-16 except that the plasticizer loading was varied from 5 wt% to 15 wt%, and the annealing step was carried out in a forced air oven. It was carried out at 100 ° C for 10 minutes and then at 110 ° C, 120 ° C, 130 ° C or 140 ° C for 10 minutes. In addition, annealing is performed to confine the film to a pair of metal frames to prevent any further shrinkage.

After annealing, the optical retardation of the film was measured. The results are shown in Table 4.

Examples 25-60 and Comparative Examples 29-64

The cellulose triacetate film was prepared by solvent casting according to the procedure set forth in Comparative Examples 1-16 except that the plasticizer loading was varied from 5 wt% to 15 wt%, and the annealing step was carried out in a forced air oven. It was carried out at 100 ° C for 10 minutes and then at 110 ° C, 120 ° C, 130 ° C or 140 ° C for 10 minutes. In addition, annealing is performed to confine the film to a pair of metal frames to prevent any further shrinkage.

After annealing, the optical retardation of the film was measured. The results are shown in Tables 5A, 5B and 5C.

The present invention has been described in detail with reference to the preferred embodiments of the present invention, but it is understood that various changes and modifications can be made within the spirit and scope of the invention.

Claims (12)

A film comprising: (a) cellulose triacetate having an ethoxylated degree of substitution of 2.8 to 2.95 (DS _{ethyl sulfhydryl} ); and (b) 5% by weight to 15% by weight based on the total weight of the film a plasticizer selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate, butyl benzene sulfonate Indoleamine, camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, epoxidized octyl tallate, polyethyl b a diol, tris(ethylene glycol) bis(2-ethylhexanoate), and mixtures thereof; wherein the film has been annealed at a temperature of from 100 ° C to 140 ° C for at least 60 minutes, and wherein at 589 nm When measured at a wavelength and normalized to a film thickness of 60 μm or less, the film has an optical retardation value (R _th ) in the thickness direction of -15 nm to +15 nm. The membrane of claim 1, which has an _{Rth of from} -10 to +10. The membrane of claim 1, which has an _{Rth of from} -5 to +5. The membrane of claim 1, wherein the plasticizer is xylitol pentaacetate, triacetin, butyl sulfonamide, camphor, 2,2,4-trimethyl-1,3-pentane Alcohol diisobutyrate, polyester adipate, octyl epoxidized octylate, polyethylene glycol or tris(ethylene glycol) bis(2-ethylhexanoate). A polarizing plate comprising the film of claim 1. A liquid crystal display comprising the polarizing plate of claim 5. A polarizing plate comprising the film of claim 4. A liquid crystal display comprising the polarizing plate of claim 7. A method for producing a film, comprising: (a) forming a dopant comprising: (i) cellulose triacetate having an ethoxylated degree of substitution of 2.8 to 2.95 (DS _{ethyl thiol} ); a plasticizer selected from the group consisting of sorbitol hexapropionate, xylitol pentaacetate, xylitol pentapropionate, triacetin, polyester succinate, butyl benzene sulfonate Indoleamine, camphor, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyester adipate, octyl epoxidized octyl ester, polyethylene glycol, tri Ethylene glycol) bis(2-ethylhexanoate) and mixtures thereof; and (iii) solvent; (b) casting the dopant onto the surface to form a wet film; (c) at least a portion of the solvent The wet film is evaporated to form a dry film; and (d) the dry film is annealed at a temperature of 100 ° C to 140 ° C for 1 minute at least 60 minutes to form a final film, wherein the final film comprises 5 based on the total weight of the film. % by weight to 15% by weight of the plasticizer, and wherein when measured at a wavelength of 589 nm and normalized to a film thickness of 60 μm or less, the optical retardation value of the final film in the thickness direction (R _Th ) is -15 nm to +15 Nm. The method of claim 9, wherein the final film has an _{Rth of from} -10 to +10. The method of claim 9, wherein the final film has an _{Rth of from} -5 to +5. The method of claim 9, wherein the plasticizer is xylitol pentaacetate, triacetin, butyl sulfonamide, camphor, 2,2,4-trimethyl-1,3-pentane Alcohol diisobutyrate, polyester adipate, octyl epoxidized octylate, polyethylene glycol or tris(ethylene glycol) bis(2-ethylhexanoate).